UF/IFAS, Horticultural Sciences Department
Vegetarian, 05-06 / June 2005
Bee Smart About Cucurbit Pollination
Phyllis R. Gilreath, Manatee County Extension Service
A. J. Whidden, Hillsborough County Extension Service
An estimated 15 to 30 percent of the food we eat directly or indirectly depends on the pollination
services of bees. Some of the crops where this is especially critical are the cucurbit crops, such as
squash, watermelon, cantaloupe and cucumber. Some wild species of bees, such as bees in the
genus Peponapis, including squash or cucurbit bees can be very efficient pollinators of cucurbits.
Honeybees, however, by virtue of sheer numbers, overwhelm the native bees and are thus the
pollinators of choice. In recent years, an estimated 50% of commercial bee colonies have been
destroyed by either disease or insect pests, such as the varroa mite, an external honeybee parasite
that attacks both the adult and the brood (Fig. 1). At the same time, wild bee populations have
also declined. While the mites that are so devastating to domesticated bee populations have much
less effect on wild bees, pesticide use and habitat loss have had a major impact. Although wild
bees will never have sufficient numbers to provide enough pollination for large commercial
crops, we still should try to encourage their presence as a type of "insurance policy".
Poor pollination, and thus poor fruit set, of cucurbits can be caused by a number of factors,
including environmental and human influences. Depending on the weather and season, host plant
flowers may be open at various times or for varying lengths of time and bees must be present
during that time. Most cucurbit flowers are only open for one day, thus environmental conditions
can be critical. Bees do not fly when it is very windy, cold or rainy. When these conditions exist,
flowers may not receive sufficient activity for optimal fruit set and/or development and may
abort. Since many cucurbit require as many as 8 to 10 bee visits for optimal pollination, fewer
visits may result in poor pollination and thus misshapen fruit due to poor seed development.
Flowers are often open very early in the morning, sometimes as early as 5:30 a.m., and are
usually closed before noon. They may close earlier if it is hotter, thus there is a very narrow time
frame for pollination to occur. Growers who really want to observe bee activity in their fields
need to be out at the crack of dawn. Much of the pollination takes place between dawn and late
morning. Wild bees will often visit first, with domesticated bees following shortly behind. Don't
shortchange the benefits of the wild bees and be sure and take into account the peak activity
periods of both wild and domesticated bees when making pesticide selection and application
Although bees can fly greater distances, they are most efficient if they can forage within about
200 yards of the hive. Hence, it helps to spread hives around a field instead of just grouping them
in one area. For large fields where the center of the field is less accessible, it may help to put
more colonies in the center-most groups along the field edge to increase competition and
encourage bees to forage deeper into the field. Honeybees typically set up a 'priority list' of
nectar sources. Some pollen is collected as a source of protein for developing bees; however, the
bees' primary task is collecting nectar. Growers can only hope that their crop is high on this
'priority list'. Often orange groves, weeds or other native species are a more attractive source.
Once bees begin bringing in nectar from a certain plant, they will continue working that type of
plant until the nectar supply is depleted, thus it is important that the target crop plant is the one
they find first.
Growers are often interested in chemical attractants to increase the attractiveness of the target
crop. In general, attractants are helpful only under marginal pollination conditions and have not
worked consistently. Remember that bee attractants encourage bee visitation, not necessarily bee
pollination. If the flowers are not appealing or there are no bees in the area, nothing will draw
them in from a distance.
Most growers have bee colonies brought in before bloom, but bees will not just sit there and wait
on the target crop to bloom. One way growers can help insure that bees work the desired crop is
to move the hives in only after the crop begins producing male flowers. Male flowers are
produced first, often from 3 to as many as 10 days before female flowers, depending on the crop
(Fig. 2). This way the bees have a source of nectar as soon as they come in and will be less likely
to look elsewhere. A good balance of blooms is also necessary, and often 3-4 times as many,
more male flowers are produced than female, but this can be influenced by temperature and day
length. Some growers have noted that with squash, bees often seem more attracted to female
flowers. This can be influenced by variety, but another factor may be the flower structure. Male
blooms have 'covered' nectaries, thus it's harder for bees to reach the nectar. Research in
Tennessee on zucchini and straight neck squash indicates that while male nectar may be 5-10%
sweeter, a greater amount of nectar is produced by female blooms, thus making them a more
productive, and possibly more attractive, source. Muskmelon blooms are visited for both nectar
and pollen, but are generally poor nectar sources. Cucumber is not a rich source of pollen or
nectar but bees readily visit it if there are no other attractive plants nearby.
There can be other factors influencing pollination. In California, cucumber pollination is often
poor when it is very hot and dry, as the pollen viability drops and pollen tube growth is affected.
Also, cucumber beetles tend to feed on the flowers and insecticides used to kill the beetles also
may kill foraging bees. The strength of the hive is also important. A colony can have as little as
10,000 to more than 60,000 bees at any one time. Recommendations in the past were for 1 hive
per acre. Most sources now recommend more hives, usually 2-3 per acre, to insure adequate
pollination. Each colony must also have adequate food supplies. Although bees may be actively
collecting pollen and nectar from a watermelon field, the overall flower density is low and they
will not be able to sustain themselves solely on this nutrient source; thus, a supplementary source
in the form of stored honey and pollen will be needed to maintain a strong colony.
While there is little a grower can do about the weather, an understanding of beekeeping practices
and bee biology will help in the decision-making process. The judicious use and timing of
pesticide applications is also an important factor. A table of common insecticides and miticides
and their relative risk to honey bees can be found online at
http://pubs.caes.uga.edu/caespubs/pubcd/b 106-w.html Growers need to be aware of the many
variables that can influence effective pollination of cucurbit crops. They should work with a
reliable beekeeper and ask questions to insure they are getting quality hives to help insure a
Honeybee on citrus blooms. Open squash bloom.
(Photo credit: (Photo credit:
Thomas Wright, UF/IFAS) Eric Zamora, UF/IFAS)
Delaplane, K. S. P. A. Thomas and W. J. McLaurin. 1994. Bee Pollination of Georgia Crop
Plants. University of Georgia Extension Bulletin 1106.
Hodges, Laurie and Fred Baxendale. 1995. Bee Pollination of Cucurbit Crops. Nebraska
Cooperative Extension NF91-50.
McGregor, S. E. 1976. Insect Pollination of Cultivated Crop Plants. USDA/ARS Handbook no.
Mussen, Eric. Extension Apiculturist, University of California, Davis. 2004. Personal
Roach, John. 2004. Can Wild Bees Take Sting from Honeybee Decline? National Geographic
News. October 20, 2004.
Sanford, Malcolm T. 2003. Beekeeping: Watermelon Pollination. UF/IFAS RF-AA091.
Skinner, John. Extension Entomologist, University of Tennessee, Knoxville. Personal
Assuring a Secure Food Supply
Mark A. Ritenour, Indian River Research and Education Center Ft. Pierce
The terrorist attacks of September 11, 2001 lead to a reevaluation of the ways our nation might
be vulnerable to attack. Attention was quickly drawn to the potential for biological attacks
(Bioterrorism) and attacks through our nation's water or food supply (Agroterrorism). It is clear
that individuals throughout the food supply and distribution chain must evaluate their operation
for potential security weaknesses and install control measure to reduce the risks of malicious
tampering. A terrorist attack originating through any operation or commodity could greatly harm
the public's confidence in the safety of that commodity and destroy the market for that product
for some time. The following are just a few of the many points to consider when developing a
food security plan for your operation:
* Create a team to asses security risks and assign one responsible person to oversee all security
* Conduct employee background checks.
* Train employees and encourage them to be alert for any signs of tampering with equipment,
supplies, or product.
* Require identification badges for all employees and visitors, and keep a record of all visitors.
* Maintain current inventories of supplies (especially of hazardous materials) and products.
* Inspect facilities and equipment daily.
* Add/repair fencing around the facility perimeter and limit entrances to as few as possible.
* Secure water sources and hazardous materials.
* Restrict access to product handling, storage, and loading and unloading areas.
* Account for all keys.
* Secure computer records and backup records regularly.
* Provide adequate lighting around the exterior of the facility.
* Use security patrols, alarm systems, and video surveillance where appropriate to continuously
monitor the facilities.
* Post emergency phone numbers and develop a plan for emergencies.
* Develop a product recall plan.
* Regularly update your food security plan.
Additional resources on food security can be found at the University of Florida's Postharvest
Programs & Information website (http://postharvest.ifas.ufl.edu) under Topical Resources:
Sanitation, Food Safety & Security. Specific recommendations and information can also be
found at the Florida Department of Agriculture and Consumer Services', Bio & Food Security
Preparedness website ( http://www.doacs.state.fl.us/bio food/) and on their Food Security Guide
at http://www.florida-agriculture.com/pubs/pubform/pdf/Food Security Guide Brochure.pdf.
In response to the September 11 th terrorist attacks, congress passed the Public Health Security
and Bioterrorism Preparedness and Response Act of 2002 (the Bioterrorism Act). The details of
the Bioterrorism Act and resulting final and interim rules can be viewed at
http://www.fda.gov/oc/bioterrorism/bioact.html While farms are excluded from the provisions
of this act, those who pack, transport, process, manufacture, distribute, receive, hold, or import
food must register with the Food and Drug Administration (FDA) and maintain records for up to
2 years detailing their food product sources and the destination of their food products. For
perishable products, records need to be kept between 6 months and 1 year, depending on the
product's perishability. Electronic registration with the FDA can be completed at
http://www.cfsan.fda.gov/-furls/ovffreg.html Alternatively, the registration form and
instructions can be downloaded from http://www.cfsan.fda.gov/-furls/papercd.html Visit
http://www.cfsan.fda.gov/~dms/fsbtac25.html for an overview of establishing and maintaining
records under the Bioterrorism Act.
Through increased vigilance and the implementation of sound biosecurity policies and
procedures, the vegetable industry can greatly reduce their risk of being targeted for use in the
next terrorist attack.
The Potato GMO Story*
James M. White, Mid Florida Research and Education Center-Apopka
In the summer of 1986, Dr. Peter Thomas was contacted by Monsanto scientists. They posed a
question: "What is the most economically important crop/virus combination in the United
States?" The answer was simple: Russet Burbank potato and potato leafroll virus. Monsanto next
wished to know if Thomas would be interested in testing the feasibility of developing virus-
derived coat protein (CP) mediated transgenic resistance in potato, the objective being to solve
potato virus disease problems in an approach that would markedly reduce or eliminate the need
for pesticides. As he was not interested in moving to St. Louis for a shortterm position, he
suggested that Dr. Wojciech K. Kaniewski might be willing to take on the assignment, after his
United States Department of Agriculture (USDA) contract as a visiting scientist in his laboratory
was completed. Dr. Kaniewski accepted Monsanto's offer and began preparations. Monsanto
assigned a group of molecular biologists to clone CP genes from different viruses and to
genetically transform tobacco and tomato plants with these transgenes, so that the first transgenic
plants would be available upon Dr. Kaniewski's arrival in St. Louis. In early 1987, Dr.
Kaniewski joined the Monsanto team in St. Louis. Large numbers of transgenic tobacco lines
were already waiting for resistance evaluation. To his great surprise, he found transgenic lines
that resisted all infections by the virus sources homologous to the transgenes under laboratory
conditions. Because they found that level of resistance did not always correlate with level of coat
protein expression, they began immediately to test all lines directly for virus resistance. As a
result, they soon found transgenic tobacco lines that were extremely resistant to tobacco mosaic
virus, alfalfa mosaic virus, and cucumber mosaic virus. This convinced them that transgenically
imparted resistance was a reality and that they should begin to generate products for tomato and
They started by showing that potato X potexvirus (PVX) and potato Y potyvirus (PVY) CP
transgenes produced high levels of resistance in tobacco. Next, they transformed Russet Burbank
with a construct containing the CP genes of both PVX and PVY (the first double gene construct)
and potato leafroll virus (PLRV) as soon as potato become transformable in 1988.Among 16
PVX/PVY transgenic potato lines produced, four were moderately resistant; one, line 303, was
extremely resistant to challenge with both viruses. Field testing between 1989 and 1992
confirmed the very high levels of resistance in line 303 under field conditions. Research into the
nature of this resistance revealed that line 303 was not infectible by either PVX or PVY by
mechanical inoculation, nor was it infectible by PVY by aphid or graft transmission, but it was
very susceptible to PVX by grafting. When plants were grafted with double infected scions, only
PVX moved freely in this potato line, convincing them that there is more than one mechanism of
There major effort was directed toward PLRV resistance in Russet Burbank. CP-expressing
plants were first generated in 1988. Although a few of these lines were statistically more resistant
than controls, none were sufficiently resistant under field conditions, which required that new
generations of plants be produced with improved CP gene constructs. Hundreds of transgenic
lines were generated from a total of 22 various PLRV CP constructs and assessed for resistance
in both the growth chamber and field trials. Many transgenic plant lines were found to be
significantly more resistant than controls, but only one of these was seen to be completely
resistant to the homologous virus strain in growth chamber experiments. Resistant lines were
field tested and their practical value confirmed, especially by virus spread tests. The only line
that was not infectible in growth chamber assays became completely infected under natural
exposure in field tests. They isolated virus from field-infected plants and retested the plants with
this isolate in the growth chamber. Although it was still immune to the homologous virus strain,
this most resistant transgenic line was shown to be completely susceptible to the field isolate,
despite the fact that the CP gene sequences of both viruses were identical. Commercialization of
the most resistant PLRV CP lines was considered but ultimately rejected, because the lines were
not good enough according to strict product standards. When the CP approach failed to produce
potatoes highly resistant to PLRV, the Monsanto administration decided in early 1991 that
research would be discontinued and the virus team disbanded if highly PLRV resistant potatoes
were not demonstrated by the end of that year. In a frantic race, five new constructs containing
the PLRV replicase region were prepared and efficacy tested. This was more desperation than
science. Two of the constructs (full-length nonmodified replicase and a truncated replicase)
delivered plants immune to the homologous PLRV isolate in growth chamber experiments. Still,
concern remained, because it was already known that TMV resistance in tobacco, as mediated by
the replicase gene, was effective only against the homologous strain of the virus. Despite this
skepticism, the new replicase potato lines were exposed in field plots at Prosser, WA to the range
of PLRV variants that occur naturally in the Columbia Basin. Although most lines were
susceptible in varying degrees, some remained virus free throughout the season. The
nonspecificity of resistance in these lines was confirmed later by field exposure of each line to
each of 64 different PLRV isolates collected from throughout the United States. They announced
the development of highly PLRVresistant potato plants in the fall of 1991 and recommended
commercialization of selected lines expressing the full-length nonmodified replicase gene. This
PLRV replicase gene was later donated to Mexico for use in a triple virus-derived gene construct
(PVX/PVY/PLRV) that would be used for triple virus protection in local potato cultivars. As the
Virus Team described its success in transgenic resistance, the Insect Control Group concurrently
announced season-long control of Colorado potato beetle (CPB) in potato using a synthetic Bt
gene. Monsanto decided to commercialize Bt insectresistant potato plants first, to later be
replaced with lines that combined both insect and virus resistance in the same germplasm. Four
local commercially important varieties were transformed with the Bt gene (Russet Burbank,
Atlantic, Snowden, and Superior). Resistant lines were selected for commercialization,
extensively characterized for regulatory approvals, and concurrentlyincreased for seed stock.
These lines were commercially available in 1995 and sold to farmers under the brand name
NewLeaf by NatureMark, a newly created Monsanto subsidiary. Based on Monsanto plans to
combine virus and CPB resistance in future products, the Virus Team began to combine CPB and
PLRV resistance, as major potato cultivation constraints in the US, in lines that would later be
named NewLeaf Plus and to combine CPB and PVY resistance in lines named NewLeaf Y. New
vectors were constructed with appropriate insect/virus gene combinations, and large-scale
transformations were begun. To expedite the selection process, it was decided to skip all
expression assays and growth chamber assays of virus resistance. All lines produced in 1993
were first subjected to CPB larva feeding test; those that survived this test were subjected to
polymerase chain reaction (PCR) screening for the presence of unnecessary backbone coding
sequences. Plant lines that passed both these tests were micropropagated and transplanted
directly to field plots. They were screened for virus resistance and agronomic performance
directly at two field sites in the spring of 1994.Based on field virus resistance, Bt protein content,
and agronomic performance 19 lines were selected for seed production and regulatory approval.
After several years of intensive evaluation, three of these Russet Burbank lines were
commercialized in 1998. During this period of field selection and evaluation, no pesticide was
ever required to control infection by any virus in the resistant Russet Burbank lines. A similar
strategy was applied to generate NewLeaf Y lines in both Russet Burbank and Shepody cultivars.
These were also commercialized in 1998.
During the process of registration, the food and environmental safety of these new products were
discussed extensively. The USDA raised, as the major problem, the issue that in transgenic
potatoes the PLRV transgene is present in all cells, whereas in potatoes infected with PLRV, the
virus is present only in phloem cells. To address this issue an experiment was designed where
PLRV RNA in individual cells could be detected with a sensitivity about 100 times higher than
that commonly achieved in immunological tests. This investigation revealed that viral RNA is
not confined to the phloem (as previously believed) but is present in almost all cells of infected
potatoes, with highest concentrations detectable in phloem cells. Moreover, minusstrand RNA
was detected in nearly all cells of infected plants, thereby demonstrating that PLRV not only
moves to cells away from the phloem but also multiplies there.
The USDA also asked for information concerning the probability of transencapsidation of
unrelated virus RNA with coat protein produced by the PVY transgene. An experiment was
designed to compare the frequency of transencapsidation of RNA of the closely related virus
potato A potyvirus (PVA) with PVY CP in mixed infections, to that of transencapsidation of
PVA RNA by PVY coat protein in NewLeaf Y potato. The results showed that the frequency of
transencapsidation in transgenic potato is at least 100 times lower than is common in natural
mixed infections. Although insect transmission of transencapsidated virions can be eliminated by
utilizing a CP gene with a single mutation, the USDA recommended use of the native CP gene,
due to the proven low probability of transencapsidation and the lack of the HC Pro gene, which
would be responsible for synergistic effects, in our transgenic potatoes.
NewLeaf Plus was commercially grown mainly in the Pacific Northwest. It produced healthy
potato crops, free of net necrosis with a markedly reduced or zero requirement for insecticide
application. Farmers and processors enjoyed most of the benefits of NewLeaf Plus, although
consumers were receiving potatoes of superior quality. The production of NewLeaf Y was
localized mainly in the central and eastern United States and Canada. It eliminated seed
reinfection by PVY in these regions which was a great benefit to seed growers. Farmers
benefited not only from higher yields of higher quality tubers in potato crops free of CPB
damage and PVY infection, but also a markedly reduced need for pesticide. Shortly after
introduction, it was impossible to produce enough seed potatoes to meet the demand. Consumer
questionnaires in the United States and Canada showed high preference for transgenic potatoes,
mainly because of their superior quality, no need for pesticide use, and competitive pricing.
Three NewLeaf Y and three NewLeaf Plus clones were approved by Canadian and United States
regulatory agencies in 1998 and 1999 and allowed for commercialization in North America.
Food and feed safety approvals of the tubers derived from NewLeaf Plus and NewLeaf Y potato
clones were obtained after voluntary consultations with the United States Food and Drug
Administration and mandatory reviews by the Canadian Food Inspection Agency, Health
Canada, the Animal Plant Health Inspection Service (APHIS) of the USDA and the US
Environmental Protection Agency. NewLeaf Plus and Y varieties have also been approved for
food export to Japan, Mexico, and Australia. NewLeaf Superior is approved for cultivation in
Bulgaria, Romania, and Russia.
Activists began their successful antibiotechnology campaign against transgenic potatoes in 1999.
McDonald's decision to ban genetically modified crops from its food chain had a major impact
within the North American potato industry. Potato processors under pressure, not only from the
McDonald decision, but also from export markets especially in Europe, were forced to suspend
transgenic contracts. Monsanto was forced to withdraw from the potato business after the highly
successful 2001 season. NatureMark was dissolved, and of course, all research toward further
potato improvement including areas of great promise, such as development of high solids, anti-
bruising, herbicide resistance, late blight and other fungal resistances came to a halt.
It is ironic that those activists who list reduction in use of pesticides as a major goal are those
that have effectively blocked the most successful scientific approach to that end.
Acceptance of transgenic potatoes in many foreign countries where cost precludes large-scale
application of effective pesticides to control virus diseases and insect pests is a highly
encouraging development. Requests for assistance continue to come from many countries around
the world. Real progress is underway to develop similar products to address regionally important
virus and insect pests.
Using Monsanto constructs, the potato virus project in Mexico has now developed new
transgenic lines of three varieties of Mexican potatoes resistant to PVX and PVY that are ready
for planting by farmers. Mexican potato lines transformed with a triple gene construct to provide
resistance to PVX, PVY, and PLRV (including the Alpha, Rosita, and Nortena varieties) are now
at the line selection stage. Furthermore, Monsanto has licensed the use of the synthetic Bt gene
for genetic transformation of six Russian (Nevsky, Lugovskoy, Elizaveta, Volzhanin, Golubizna,
and Charodei), three Bulgarian (Kalina, Koral, and Bor), and three Romanian (Redsec, Coval,
and Belint) leading potato varieties for CPB resistance. In Russia and Bulgaria, two years of field
tests for line selection have been completed, and tests required for varietal registration are now in
progress. In Romania, transgenic lines have been transformed, and the first line selection field
tests are now under way. NewLeaf Plus and NewLeaf Y were recently tested for virus resistance
on Mauritius, and the virus resistance of these lines has proven to be highly effective in this
remote region, which means that existing products could be cultivated there, or the genes could
be used for transformation of local varieties.
This 'story' was taken from: Kaniewski, Wojciech K. and Peter E. Thomas.2004. The Potato
Story. AgBioForum, 7(1&2): 41-46.
New Record-Size Tomato
James M. Stephens, (retired), Horticultural Sciences Department
Debbie Doll and Walter Ross grew a record size tomato in Palm Beach county. It is of the
'Brandywine Red' variety and weighed in at 3 lb. 4.3 oz. Although retired, Jim Stephens still
keeps up with Florida's biggest vegetables as one of his Emeritus Professor duties. The system
he employs still requires the assistance of Extension agents in each county following guidelines
established in1989. Prior to that year, no one kept records of big vegetables grown in Florida.
Palm Beach County holds the most Florida records with 12 out of the 53 kept. The runner-up is
Suwannee County with eight records. The following is a list of the current record-size vegetables
in Florida (through May, 2005).
Florida Record-Size Vegetables
UF/IFAS, Horticultural Sciences Dept.
Jim Stephens Retired (352)392-2134 x226
(Last update May 2005)
Okra, pod (wt)
Okra, pod (length)
La. Green Velvet
8 Ib. 1 oz.
12 Ib. 10 oz.
5 Ib. 4 oz.
20 Ib. 9 oz.
35 Ib. 3 oz.
3 Ib. 1 oz.
15 lb. 4 oz.
15 lb. 6 oz.
1 Ib. 3 oz.
13 ft. 3 in.
4 Ib. 7 oz.
2 ft. 3 in.
2 ft. 6 in.
4 Ib. 8 oz.
1 Ib. 8 oz.
3 Ib. 7 oz.
5ft. 1 2 in.
11 lb. 2 oz.
21 Ib. 8 oz.
19 Ib. 8 oz.
3 Ib. 10 oz.
29 Ib. 15 oz.
80 Ib. 13 oz.
20 Ib. 4 oz.
1 ft. 10 4 in.
19ft. 10/2 in.
3 Ib. 11 oz.
1 Ib. 3.84 oz.
2 Ib. 13 oz.
44 Ib. 2 oz.
3 Ib. 12 oz.
23 Ib. 5 oz.
36 Ib. 8 oz.
131 Ib. 12 oz.
23 Ib. 12 oz.
3 Ib. 12 oz.
47 Ib. 9 oz.
14 Ib. 10 oz.
16 Ib. 6 oz.
6 Ib. 2 oz.
3 Ib. 4.3 oz.
21 Ib. 11 oz.
12 Ib. 15 oz.
4 ft. 4 in.